i have just finished doing this myself!
get a stout pair of pliers and with a bit of effort you can twist the hook thingies that the ends hinge on and pop the ends out (mind your fingers!) then i fixed them together with cable ties. i am surprised at how rigid the new big crate is. my 3 little girls are now bombing up and down their 8 foot crate. when little robbie goes of to his new home, i am thinking of joining his 4 foot crate on as well, though i would imagine i will need to build a timber frame to support a 12 foot crate.
joining the 2 has just taken me and a friend just 10 minutes. hopefully i will be able to put a shelf in at either end in the next few days too.
now it is 12.45 pm and i am going to bed!